1. Field of the Invention
This invention relates to load distributing or reinforcing fittings which more widely distribute lateral stresses applied to wood members at the location where the wood is bolted to another member.
2. Description of the Prior Art
In the past, the bolting of a wood member to another member, whether to concrete, to steel or another wood member, particularly when the bolted wood member is structural in application, required a relatively large bolt shank diameter in order to gain sufficient strengths during pulls and stresses of the wood against the shank of the bolt. Typically, when a given size steel bolt is specified and used to connect a structural wood member to another structure, the bolt shank is passed through a hole in the wood and fastened to the other member such as with a nut or is embedded in concrete to secure the wood member in place. The diameter of the steel bolt which is typically used provides several times more bolt shear strength than is required for the particular application, as the wood will split long before the bolt shank will shear. The diameter of the bolt provides more than just shear strength, also providing surface area for the wood to abut against under lateral loading, and therefore the size of the steel bolt shank is oftentimes not so much determined by the shear strength of the steel bolt itself, but rather by the required surface area of the bolt shank that the wood may abut during lateral loading. Insufficient bolt shank surface area provided against the wood during lateral loading will lead to the wood failing, and typically the failure of the wood will occur substantially prior to the shearing of the bolt shank.
In other words and for example, often a steel bolt having a 1/2" shank diameter will have far more than adequate shank shear strength for a given connection, however, load and stress calculations will call for a 1" diameter bolt in order to acquire adequate overall strength particularly during lateral loading. In this application, the 1/2" diameter bolt shank would be quite adequate from a bolt shear strength standpoint, however, the surface area of the 1/2" bolt shank to which the wood may abut is inadequate to provide the necessary connecting strength prior to the wood failing under lateral loading. The reason the 1" diameter bolt would be used is because the 1" diameter shank provides a much wider or greater surface area for the wood to abut against under lateral pulls (transverse to the lengthwise axis of the bolt shank) than the 1/2" diameter bolt. The much wider or greater abutment area provided by the 1" diameter bolt shank provides a greater distribution of load (stress) to the surrounding wood compared to the 1/2" bolt, and therefore the connection as a whole is stronger.
As bolt sizes increase, they rapidly increase in cost, and for example, a 1" diameter bolt is several times more expensive than a 1/2" diameter bolt of the same length. Additionally, 1" nuts and washers are also quite a bit more costly than 1/2" nuts and washers.
Therefore, it would be desirable to be able to standardize and utilize smaller and thus less expensive bolts to bolt wood structural members if adequate overall strength could be obtained. Additionally, current bolt shank sizing practices normally require the stocking of various bolt shank diameters on a construction site, and it would be desireable to reduce the number of different bolt sizes which would need to be stocked.